The present invention relates to a strong threaded bushing or insert of open or closed construction with symmetrical or asymmetrical trapezoidal external thread and internal thread, which insert is screwed via its external thread into a, preferably metallic, workpiece that has a corresponding internal thread (female thread), with the internal thread of the threaded insert serving to receive a high-strength screw that has a corresponding opposing or cooperating thread.
In screw connections having a female or internal thread directly in the material of one of the mating parts that are to be screwed together, threaded inserts are often used for the following reasons:
(a) the strength of the basic material is not sufficiently durable for the female thread, with this frequently being the case when using high-strength screws; PA1 (b) the thread has to have special resistance to wear and great reserves with respect to durability since the screw connection is often repeatedly loosened and retightened, as a result of which incorrect, in particular impermissibly great, tightening of the screw has to be allowed for; and
(c) the female threads of particularly large, expensive components have been produced defectively or do not produce a seal after final machining in the case of parts that have to be tight to liquids or gases. In these cases, expensive rejects or scrap can be avoided by introducing a larger female thread and installing a suitable threaded insert without altering the screw itself.
Threaded inserts of sturdy, suitably thick-walled construction or, if a seal with the female thread is unimportant, trapezoidal wire profile inserts, for example "Heli-Coil" inserts, have proven suitable for the above-mentioned cases. Unfortunately, inserts of this type cannot be used if:
(1) the external diameter of the threaded insert has to be small due to the restricted space or to avoid impermissible weakening of load-bearing structures, while at the same time providing a sealing relative to the female thread; and/or
(2) wire profile inserts having small external diameters are not available, for example in an asymmetrical design, due to the use of special threads or if the female thread has to produce a seal.
It is therefore an object of the present invention to construct a threaded insert of the aforementioned general type in such a way that it has a small external diameter that is adapted to the restricted space and thus prevents impermissible weakening of load-bearing structures. At the same time, the insert should also be suitable for special threads (for example of asymmetrical design) and should simultaneously ensure that the female thread produces a perfect seal (in the case of a closed construction).